PSI - Issue 37

Mohammed Algarni et al. / Procedia Structural Integrity 37 (2022) 676–683 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

682

7

Figure 4: Influence of mean stress accurately predicted by the Walker fatigue life model for LN specimens.

5. Conclusion The uniaxial fatigue behavior of PLA specimens was studied through extensive load-controlled fatigue tests. Three fatigue load ratios (R = -1, 0.1, and 0.3) were considered on specimens with three notch sizes: large, medium, and sharp notches. Based on the theoretical analysis and experimental outcomes in this work, the conclusions below are set: • All specimens were 3D printed with fixed printing parameters and handled as homogenous and isotropic. Therefore, the influences of the printing parameters and environmental temperature were not considered in the current research. • The existence of notches significantly reduced the fatigue life of PLA material by more than 55%. • The fatigue life under the influence of notches was modeled by KV Model. The notch effect was poorly predicted by the fatigue notch factor. However, it was accurately predicted by the stress triaxiality factor. • Similar to the effect on metals, the mean stress influence on fatigue life of the PLA specimens was significant. The fatigue life was reduced by more than 40% by increasing the load ratio from 0 to 0.1. However, no significant effect on the fatigue life was noticed by increasing the load ratio from R = 0.1 to 0.3. • Modeling the fatigue life under the influence of mean stress was performed by the Walker model. The results show a precise correlation with the experiment data. References Afrose, M. F., Masood, S. H., Iovenitti, P., Nikzad, M., & Sbarski, I. (2016). Effects of part build orientations on fatigue behaviour of FDM processed PLA material. Progress in Additive Manufacturing, 1(1), 21-28. Ahmed, A. A., & Susmel, L. (2018). A material length scale – based methodology to assess static strength of notched additively manufactured polylactide (PLA). Fatigue & fracture of engineering materials & structures, 41(10), 2071-2098. Ahmed, A. A., & Susmel, L. (2019). Static assessment of plain/notched polylactide (PLA) 3D ‐ printed with different infill levels: Equivalent homogenised material concept and Theory of Critical Distances. Fatigue & fracture of engineering materials & structures, 42(4), 883-904. Algarni, M. (2019). Notch Factor Correction Using Stress Triaxiality of Plane-Stress State in High-Cycle Fatigue. International Journal of Fatigue, 128, 105204. Algarni, M. (2021). The Influence of Raster Angle and Moisture Content on the Mechanical Properties of PLA Parts Produced by Fused Deposition Modeling. Polymers, 13(2), 237. Algarni, M., & Ghazali, S. (2021). Comparative Study of the Sensitivity of PLA, ABS, PEEK, and PETG’s Mechanical Properties t o FDM Printing Process Parameters. Crystals, 11(8). https://doi.org/10.3390/cryst11080995 Amjadi, M., & Fatemi, A. (2020). Multiaxial fatigue behavior of thermoplastics including mean stress and notch effects: Experiments and modeling. International Journal of Fatigue, 136, 105571. Awaja, F., Zhang, S., Tripathi, M., Nikiforov, A., & Pugno, N. (2016). Cracks, microcracks and fracture in polymer structures: Formation, detection, autonomic repair. Progress in Materials Science, 83, 536-573.